The present invention relates to a process for making ferroboron, and in particular a ferroboron which contains some silicon, but is substantially free of aluminum.
In the past, aluminum-free ferroboron has been expensive. While aluminum containing ferroboron has been satisfactory for many applications, some applications (and particularly processes for producing amorphous magnetic alloy) cannot generally use such aluminum containing ferroboron.
Amorphous alloys, such as an iron-3% boron-5% silicon (typically also containing about 0.5% carbon) have been suggested for a number of magnetic applications, such as in motors and transformers. Such alloys have been relatively expensive, however, principally due to the cost of aluminum-free boron. The boron content for such magnetic alloys typically has been added in the form of ferroboron which has been prepared by carbon reduction of a mixture of B.sub.2 O.sub.3, steel scrap, and/or iron oxide (mill scale). That process for making ferroboron is highly endothermic and is typically carried out in submerged electrode arc furnaces. The reduction requires temperatures of about 1600.degree.-1800.degree. C. and the boron recovery is low (typically only about 40%, and thus about 2.5 times the final amount of boron must be added) due to the very high vapor pressue of B.sub.2 O.sub.3 at such high reaction temperatures. Furthermore, large amounts of carbon monoxide gas are evolved during the process, necessitating extensive pollution control. Low recovery of boron and the use of extensive pollution control equipment result in a high cost of converting B.sub.2 O.sub.3 (anhydrous boric acid) into ferroboron. Such ferroboron typically costs more than 5 times as much as boric acid per pound of contained boron.
Although boric acid can be reduced by an aluminothermic process, such as a process produces ferroboron with about 4% aluminum which, although suitable for some applications, is unsuitable for use in magnetic applications.